Questions tagged [moment]

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Calculating the moment/torque of a force applied over an area

This diagram shows a current carrying wire (from PQ) and a uniform magnetic field applied across the wire (from 85-90 cm) into the page, therefore the force is upward. How would one calculate the ...
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Are there physics theorems that can prove maths theorems? Eg Pythagoras' Theorem

There's this recent post on maths overflow Which theorems have Pythagoras' Theorem as a special case? that has an answer by dxiv that appears to use a physics theorem to a prove a maths theorem, ...
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Are these two torques identical? [closed]

Hello, I had this question in a MCQ. According to the solution, these torques are indeed identical but I don't understand how. I tried to decompose $\overrightarrow{AB}$ into $\overrightarrow{AC} + \...
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Why do references use different variables in the differential of moment of inertia?

I see formulas in moment of inertia that use mass, area or volume as the differential in moment of inertia. I do not have a good grasp of the concept. The variation in formulas just confuse me. Can ...
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4 answers
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Why don't simple machines change the amount of energy needed?

Suppose I wanted to tighten a nut and I do so using two spanners of different arm lengths, say of $10 \text{ cm}$ and $20 \text{ cm}$. According to a an online source: A spanner counts as a simple ...
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The moment of inertia of a hollow cylinder is lower than that of the "corresponding" solid cylinder (same density, outer radius, height):

This is a self-answered "question" for those scratching their heads after learning, e.g. in class, that the moment of inertia of a hollow cylinder is higher than that of solid cylinder. Note ...
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Deformation convert stresses to others

Elastic instability (also known generically as buckling) can be interpreted as the phenomena in which deformation converts axial stress(compression) into bending moment. OK. Also, if we deform an ...
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Best place to shoot an object to topple it

Imagine a carnival game, the ones where you have to shoot down items with a toy gun, my question is where to shoot the item to maximize the rotational moment of the item. My studies lead me to believe ...
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Determine the coordinates of the point on the $y$-axis that the force passes

I've recently done a problem where I've been given adiagram with some forces applied to a beam trolley, and where I needed to determine the coordinates of the point on the $y$-axis through which the ...
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Why does a long, free-to-move object rotate when I push it from one side?

I was pushing a pencil along a table top when I noticed that it rotates around the other end. Somewhat like this(The dotted red lines show the final position of the pencil). The pencil is not pivoted ...
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Why does it matter where you take moments, when its a lamina?

I've just been doing moments on laminas for the first time and I think I've missed something crucial. If I take moments around point $X$, I get: Clockwise: $30\ \mathrm N$ with a perpendicular ...
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Is this formula for finding the balancing point correct?

Suppose I have a uniform meter rule in which there are a number of weights $w_1,w_2,w_3,....,w_n$ suspended at points $p_1,p_2,....,p_n$,respectively and the meter rule itself has a weight $w$ that ...
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What does the 2nd moments equation in the discrete ordinates method mean?

https://www.comsol.de/blogs/heat-transfer-in-participating-media-and-the-discrete-ordinates-method/ In the discrete ordinates method (see above) there are three (0th, 1st, 2nd) moments equations to ...
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Question about moment with two springs and one weight

The answer to this question is C. I got to it by realizing that if the weight is moved away from the pivot then it will produce an anti-clockwise moment which will cause X to decrease and Y to ...
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Meaning of torque

So, in the diagram, A is the axis of rotation and the net moment from the forces acting there(as shown) is 6Nm.The moment is due to the forces acting in the direction as shown and the moment the ...
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Why does rotation happens about hinge point in a vertical bar when net force acting on it are zero? [closed]

As we know that if the net external force on a body is zero its center of mass will be at rest and also rotation will happen about center of mass only but in this hinge and rod case it is clear by ...
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1 answer
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Sliding arm problem, locking and singularity

I posted a version of this earlier but I feel like my problem was not very clear so I hope that this explains what is so confusing here. Shown in the image is a view from above, of an arm that's ...
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Why does a body rotate faster if force is applied away from the pivot?

Why does a body rotate faster if force is applied away from the pivot? I need an intuitive answer to this. Like why does a door rotate slower if I push at it closer to its hinge, or faster if I push ...
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How to determine the direction of moments (confusion)?

My teacher is showing me a few ways that I can calculate moment and its direction. In this example, she is going to use the principle of moments to solve this (ie resolving into components) But what ...
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1 vote
1 answer
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How is the "wrench" a simplification for a general force-couple system? [closed]

from engineering mechanics, by beer and johnston For any system of n forces, we can simplify this system to a Force-Couple system. The simplification is intuitive- we don't need lot of forces just a ...
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Is there a system that only contains electric dipole moment but not higher electric multipole moments?

Does there exist such thing, if it does, which charge distribution could generate it? If it doesn't exist, can it be proven?
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Are there higher moments of vector quantities?

The $n$-th moment of mass of a point mass $m$ with respect to a point located at $\boldsymbol r$ is $$ \mu_n(m) = m\boldsymbol r^n $$ So the 0th moment is the total mass $m$, the 1st moment is $m\...
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1 vote
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Overturning torque on a car navigating a curve

The car shown above with mass M is turning to the left with an uniform angular speed W on a circular path with radius R. When the angular speed is increased to a critical value C, one of the normal ...
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How is there moment for a group of forces which its resultant equals zero?

I am a beginner in mechanics, and when I was introduced to moments there was a theorem that says "if a set of forces acting on a rigid body has a resultant, then the algebraic sum of these forces ...
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What does the dipole moment really represent?

Wikipedia gives the most general expression for the $n^{\rm th}$ moment $\mu_n$ of a physical quantity $\Lambda$ as: $$ \mu_n = \int {\bf x}^n \space \lambda({\bf x}) \space \rm d^3 x$$ provided that ...
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What exactly is moment? Why does it correspond to a rotation?

Wikipedia says: Moment is an expression involving the product of a distance and physical quantity. I don't quite get it. Moment is a vector, the cross product of the distance vector and the vector ...
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Moments by normal stress

I am a bit confused with the following formula why is that the normal stress ($z$), not the normal stress ($x$), is involved in the formula for the moment around $x$, $Mx$? Likewise, My also equals ...
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What is mass moment? [duplicate]

My teacher gave the following definition while teaching chapter "Center of mass": "It is defined as the product of mass of the particle and distance of particle from point about which ...
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2 votes
2 answers
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Does "moment" have a single meaning in physics?

I am a high school student and I am curious about the word moment and what it means in different contexts, whether it has a definite meaning or not? I know it has some relation to different kinds of ...
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2 votes
4 answers
551 views

What are the proper definitions of moment, couple, torque, 'moment of force'?

When I read some scientific articles I am getting confused with the interchange being used between Torque, Couple, Moment, 'Moment Of Force'. Have I got this correct? Moment is supposed to be some ...
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Is the angular acceleration of a rigid body independent of the reference point?

I'm solving this particular question (refer to image) in which a rod is released from equilibrium after one of the two springs to which it is initially connected is disconnected. In order to calculate ...
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2 answers
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Why does the Larmor precession frequency depend on $\vec{B}$ instead of $\vec{H}$?

From what I know: The magnetic field strength, $\vec{H}$, is the field generated by a free current flowing on an electric conductor. The magnetic flux density, $\vec{B}$, is a response of the medium ...
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Intuition behind First moment of area and link to centroids

I essentially have the same question, however only concerning the First moment, as this user ,however none of the answers satisfy my questions. I understand that we are trying to get a sense of the ...
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2 answers
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A problem about moment (torque ) [closed]

Everybody knows that moment of a force increases with distance. However, there is a problem about it that makes me confused these days: Let's take a look at this picture due to the formula M = F.d, ...
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Physical meaning of internal bending moment

Here's the setup: The textbook, where this is from, first walks through how to find the strain and stress as a function of z, which is fairly straightforward. Then, it calculates the "total internal ...
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1 answer
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When calculating first moments of mass in cylindrical coordinates, can we use $r,\theta$ instead of $x,y$?

Usually when we want to find the center of mass of a 3D body, we need to find the first moments of mass about $x,y,z$, call them $M_x,M_y,M_z$. Defined by $$ M_x = \iiint x\rho \ dV, $$ where $\rho$ ...
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Finding distance of forces for maximum bending moment

I'm having a hard time looking for the distance ($x$) on which the forces must be located for a maximum bending moment. The reaction forces in $A$ and $B$ are dependant of the value of $x$, and so ...
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2 answers
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Why does the load cause a moment around the support point in column buckling?

Here is a picture from Wikipedia, a free body diagram used to derive the maximum load in Euler's buckling theory. The moment is calculated around point A. It is claimed that the load $P$ causes a ...
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Finding the moment at an angle [closed]

The question wants me to calculate the moment exerted on the nut, and the force (20 N) is applied at an angle (30 degrees) towards the pivot. I tried redrawing this as a triangle, with an angle of 30,...
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1 vote
1 answer
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Simple model for friction in a pivot joint

Consider a pendulum that is attached to its pivot point using a hinge or ball bearing joint. What is a simple but reasonable approximation for modelling friction in that joint? Background: I'm ...
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Can we construct a (specially designed) truss that is horizontal when supported from one end?

It is not possible to support a horizontal beam from one end, and the same is true for an I-Beam. I believe this can also be proven for a pipe, but that proof is just outside of my reach. But all of ...
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How to take moment about point of contact in a hemisphere?

In question 3, i am able to solve first part but in second part i don't know how to take moments about point of contact or about center ?
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What is a mass moment?

I am currently reading through a document Finding Moments of Inertia from MIT, page 4, and I am a little confused as to one of the concepts that they use. In this document, there is mention of a mass ...
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3 answers
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Equilibrium of a body in torque problem

I was watching a video about torque in which the task was to find the force $F_2 $ when a body is in equilibrium. The person in the video said that in order for the body to be in equilibrium, two ...
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A bar weighs $2N$ and is $5m$ in length. What is the weight needed to balance the bar?

A bar weighs $2N$ and is $5m$ in length. What is the weight($M$) needed to balance the bar? I think I understand that the equation not including the weight of the bar would have $$3*3=(5*1)+(2*M)\...
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Moment on a body and on a simply supported beam

Consider a body on a frictionless floor being acted upon by a force F as shown in figure. Force acts on its centre of mass. (Centre of mass and centre of gravity coincide in this case, ie, both lie on ...
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Difference between torque, moment and couple

I know the basics of them like Torque is force multiplied by the distance (from the point where there is no rotation like centre of gravity). Couple acts because of two equal and opposite forces ...
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1 answer
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Teeter Totter Team Building Game

I recall doing a team building exercise where a team of about 4 people needed to balance a teeter totter, so that neither of the ends was touching the ground. They could achieve this by having the ...
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Can someone prove the Principle of Moments from Newton's Laws?

Is it possible to rigorously proof the Principle of Moments from just Newton's three laws? Here's my formulation of the laws/axioms? Someone tell me politely if I'm wrong. Particles always follow ...
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Ratchet handle force calculation

I have strap ratchet which is being pulled on both sides with some force(say 500lb). Could some one please help me know the force to be applied on the handle of the buckle to open it? Can anyone ...
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